Effects of HCO₃^– on Degradation of Toxic Contaminants of Emerging Concern by UV/NO₃^–

Abstract

This study investigated the significant influence of HCO3– on the degradation of contaminants of emerging concern (CECs) during nitrate photolysis at 254 nm for water reuse applications. The second-order rate constants for the reactions between selected contaminants with carbonate radical (CO3•–) were determined at pH 8.8 and T = 20 °C: estrone ((5.3 ± 1.1) × 108 M–1 s–1), bisphenol A ((2.8 ± 0.2) × 108 M–1 s–1), 17α-ethynylestradiol ((1.6 ± 0.3) × 108 M–1 s–1), triclosan ((4.2 ± 1.4) × 107 M–1 s–1), diclofenac ((2.7 ± 0.7) × 107 M–1 s–1), atrazine ((5.7 ± 0.1) × 106 M–1 s–1), carbamazepine ((4.2 ± 0.01) × 106 M–1 s–1), and ibuprofen ((1.2 ± 1.1) × 106 M–1 s–1). Contributions from UV, reactive nitrogen species (RNS), hydroxyl radical (•OH), and CO3•– to the CEC decomposition in UV/NO3– in the presence and absence of HCO3– were investigated. In addition, possible transformation products and degradation pathways of triclosan, diclofenac, bisphenol A, and estrone in UV/NO3–/HCO3– were proposed based on the mass (MS) and MS2 spectra. Significant reduction in the cytotoxicity of bisphenol A was observed after the treatment with UV/NO3–/HCO3–.